What I have noticed as this:
Take 5k races for the first example:
People who run over 20 tend to be overweight
People who run 17-20 tend to be average or on the heavier side
People who run 15-7 tend to be on the below average to average size
People who run sub 15 tend to have that "runners look": very thin, almost evacuated looking, yet are extremely fit
What I've noticed as well is all these runners tend to have the same diets. In fact, the guys who run really fast, sub 15, tend to eat junk, no healthier, and even more of it! Yet they are very lean. Something about running fast changes the body.
Take marathoners as well:
People who run over 4:00 tend to be overweight
People who run 3:00-4:00 tend to be average or on the heavier side
People who run 2:40-3:00 tend to be a little below average or average
People who run sub 2:40 tend to be very lean, and let's not even get into sub 2:20!
Yet diets remain the same.
So what I am saying is no way is it all calories in versus calories out in the end. These people who train more have to eat more obviously to prevent injury, worse performance, and to keep improving as you need the calories aka energy
BUT I think there is something to making your body run FAST that causes certain metabolism shifts to take place. Your body *just without changing anything* will lean up to make running more efficient on itself. It adapts to its environment. People that jog 100 miles per week at 10:00/mi won't be nearly as lean as people running 100 miles per week at 6:00-7:00/mi, despite eating the same foods and in fact even more calories to make up for the greater energy expenditure. Something about fast running...
You can see this is people who start running, get faster, and never change their diets (like most of us). I've seen people eat standard junk diets and start off overweight and running 25 for 5k, and without changing their diet begin to lean up and run 15 over the course of years. When they get hurt if their diet doesn't change they gain weight. Whether it's due to their body not needing to stay lean anymore to make running (or lack thereof) easier or because they eat poor diets is up for debate. May be both.
So there is something to running fast that makes your body "adapt to its environment" if you will.
Thoughts?